Such a horn assembly for a rotary sealer is known from the co-pending international application PCT/DK2006/000163, which at the time of filing of the present application is not published.
Typically, in addition to the said one support the horn or the booster connected thereto is provided with a further support arranged a multiple of half a wavelength, e.g. half a wavelength of the applied vibrations, from the said one support and is thus arranged in a point with minimum vibration amplitude in the longitudinal direction. In these points with minimum vibration amplitude in the longitudinal direction, the radial displacement reaches its maximum or is close to reaching its maximum when the horn vibrates.
Furthermore, rotary sealers typically comprise an anvil, e.g. an anvil roller, being rotatable in opposite direction of the horn and having a peripheral face adjacent the sealing face of the sealing horn. The part(s) to be sealed—typically of a thermoplastic material—is/are inserted between the sealing face of the horn and the peripheral face of the anvil roller, sealing being provided due to the vibration of the sealing face of the horns and the pressure exerted between the sealing face and the peripheral face of the anvil roller.
As mentioned, maximum radial movements occur in the points with minimum vibration amplitude. Accordingly, it is vital that the supports are resilient. If the supports are not suitably resilient, a large amount of energy is transferred to the hollow shaft and the housing which otherwise would be utilized in the sealing process. Furthermore, increased mechanical wear arises between the supports and the hollow shaft, if the supports are not adequately resilient. As a result, the rotary sealer operates unevenly with reduced precision and reduced operating life. Additionally, an insufficiently resilient support will cause intense heating of the support areas and at worst may result in the supports being welded to the hollow shaft and/or the retaining means.
For sealing thick materials and/or sealing at high velocities, a substantial amount of energy, high amplitude and a comparatively high pressure between the sealing face of the rotating horn and the material to be sealed are required. The high radial pressures or, when sealing at high velocities, centrifugal forces acting on the slightest imbalance in the horn will result in a bending of the horn assembly. Further in order to obtain viable seals, the peripheral sealing area of the horn must rotate within tolerances better than a few micrometers
Known rotary sealers do not allow for sealing under the above operating conditions without compromising the required precision and without large amounts of energy being dissipated in the hollow shaft and the housing resulting in energy loss and a risk of welding the support to the hollow shaft.